A geometric correction method, conducted by capturing an image projected by a projector with a camera and using the captured image, has been available to correct a projected image to match the projector position and attitude, a projection plane shape, and so on to reduce distortion of the projected image and achieve alignment between images projected by the plurality of projectors. Such a method required finding corresponding points between the projected and captured images.
As a method of finding corresponding points, ISL (Imperceptible Structured Light) was proposed that conducts sensing during content viewing (refer, for example, to NPL 1).